Evil Hal Mason couldn't blend in forever on "Falling Skies." In this Sunday's episode of the TNT drama, Drew Roy takes on his biggest acting challenge of the season, as Charleston finds out that his character, Hal, is no longer an honorable fighter for humanity, but an alien-controlled traitor.

Previews TNT aired at the end of last Sunday's episode revealed that Evil Hal will be taking his dad, Tom Mason (Noah Wylie), hostage and demanding (for Espheni Overlord Karen) all the information he can get about the device the Volm are building.

With Season 3 packed with so much heart-racing alien invasion drama each week, AccessHollywood.com caught up with Drew to see what he could hint at about what's ahead in Sunday's huge Hal episode, "Be Silent and Come Out." He also tackled our questions about what Hal did with his step mom, Anne Glass (Moon Bloodgood), and whether we'll know which side the Volm are really on by the end of the season.

AccessHollywood.com: TNT is billing this Sunday's episode as the one 'everyone will be talking about.' How big is it?

Drew Roy: It's the biggest storyline they've written for me in the three seasons, so I felt quite honored that it was as awesome and intricate as it was, especially with it being on the back end of this three episode arc of this evil Hal character. I like to think of it as being pretty big, but when we were shooting it, it was just day by day and doing the work, and having a blast doing it.

Access: The previews actually show Hal holding his father, Noah Wylie's Tom Mason at gun point, what can you hint at?

Drew: We've seen this new side of Hal that is now very confident and trying to put at ease all of these feelings he's been having for the first couple [of] episodes [where he was] telling people that things are wrong. Now, he's just turned on a dime and feels like everything's fine because he's been, I guess you could say, taken over by Karen. At the end of this last episode, we saw that Ben - Hal forgets that Ben is as connected to the skitters as he is so his plan could potentially get leaked out if the word comes back that I am this supposed mole, and he has to step things up into high gear, and he has to make a few decisions that aren't the most calculated. I think he was planning on having some more time and has to make some rash decisions and finds himself in some pretty tricky situations - with a hostage, who happens to be his dad.

Access: How excited were you when you learned this big story was coming? Did they tip you off early on in the season that there was this big script coming?

Drew: When we actually shot the scene at the end of last season, when the bug crawls into my ear, we had no idea what was gonna come of it. We just knew it was creepy, it was interesting, it opened up the door for something, but we didn't know what that something was. It wasn't until Comic-Con, I guess it was two months before we were going back and shooting, that Remi Aubuchon, who's the head writer for the show, approached me and said, 'Look, I think we've come up with what's gonna happen. Hal is gonna be paralyzed.' I was like 'Oh, well that's interesting. For how long?' I was like, 'I kind of like throwing the guns around and all that stuff.' I'm saying this jokingly because as an actor, that's the kind of stuff that you wanna have happen. ... It's a different side to the character, so I was really intrigued about that, and I'd say it was ... about five or six weeks into shooting that I heard that the sixth hour was going to be a big one for me and that it was gonna involve this evil, devious side of Hal and I was about as excited as you could get. [I was] very intrigued as to how it was going to come together, but I'm always up for the challenge.

Access: I've gotta ask -- what did you do with Anne and your baby sister?

Drew: (laughs) It's a good question. ... I don't even know if I know. I'm gonna blame it on the fact that it was evil Hal, so good Hal never really knew, but it's a good question. He took them, he sent them somewhere, but who knows!

Access: What's been the reaction from fans to the duality of your character?

Drew: Well, it's funny. There's a couple of different things people will say. One of them is they find this new Hal interesting, but they miss the old Hal that they all loved. Some people absolutely love the new Hal, the evil Hal, and they say that he's more fun to watch and then some people just say that the new Hal is just sexier (laughs) and therefore they don't know what to think about it because they hate the character, but they like watching.

Access: I have to ask you about the Volm. Will we know by the end of the season if they are good or bad or somewhere in between?

Drew: We will know by the end of the season and with the storyline that I have going on with Hal, I never really had to put much thought into where the trust lies with the Volm because there were bigger issues on Hal's plate at the time. But for the other characters, we were constantly wondering what are they trying to do, why is Tom kind of being a little secretive with the information he's giving, what is Marina up to, why is she all over this and at this point in the season you're supposed to be as confused as you are and just wonder along with the rest of the cast as to what they're doing and what will come of it.